Problem setting up ADC in 16F690 mcu

arunb · Joined: 08 Sep 2003 Posts: 492 Location: India

MCU: 16F690
Compiler: PCM 3.228

Hi,

I use the code below to setup the ADC of the 16F690 mcu.

ECACE · Joined: 24 Jul 2006 Posts: 94

Couple of things:

1) You have not defined CHN_LED_INTENSITY

2) You have not defined fTmp

3) In your hardware, do you have floating pins? If so, you should tie any floating pins to ground via say 2.2K. Floating pins have a way of reacting erratic.
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arunb · Joined: 08 Sep 2003 Posts: 492 Location: India

I have extracted the relevant parts from the main program code,

CHN_LED_INTENSITY is 0 this defines the channel number of the ADC.

#define CHN_LED_INTENSITY 0

fTemp is a float value.

I believe the ADC is not setup properly, it seems I am missing out on some thing.

Kindly explain what you mean by floating pin, isn't the ADC pin supposed to be floating, but in my case the pins shows a steady voltage of 5.4 V DC !!

I wonder why ??

thanks
arunb

Ttelmah · Guest

Think about it for a moment.
The PIC _cannot_ 'generate' an output above the voltages present on it's pins (the only internal 'voltage generator', is the programming voltage generator for the flash memory, and this is itself 'slaved' to the voltage on Vpp). If you are seeing '5.4v', it implies _either_, that a voltage above 5v, _is_ being presented to the pin (most likely - triple check for a short somewhere...), _or_ that another pin is being pulled to a higher voltage, and with the internal protection diodes, is _raising_ the supply the PIC is internally using. Both scenarios, are external wiring faults, not faults with the code.
Though there may be faults that will stop the ADC working, _none_ can generate voltages above the supply rail. You need to find what is generating the 5.4v signal, bfore proceeding...

Best Wishes